Abstract Clear cell type renal cell carcinoma (CRCC), the most prevalent form of kidney cancer, is among the most resistant of tumors to traditional chemotherapy and radiation. It has become established that CRCC is uniquely driven by the hypoxia-inducible factor (HIF)-2?, whereas the closely related HIF-1? plays a tumor suppressor role, and is frequently deleted in advanced tumors. Since HIF-2? is rarely detected in normal, well perfused tissue, the selective inhibition of HIF-2? is an attractive therapeutic strategy for CRCC. Through a high throughput screening campaign, Kuda Therapeutics has identified a series of compounds that specifically decrease HIF-2? protein without affecting HIF-1?. This provides a dual and profound benefit by inhibiting both the transcriptional and non-transcriptional targets of HIF-2?. The compounds act by enhancing the binding of iron regulatory protein (IRP)-1 to the iron-responsive element (IRE) within the 5? untranslated region of HIF-2? mRNA, which blocks HIF-2? translation. Multiple rounds of structure activity relationship (SAR) analysis have identified a lead chemotype of which K1299 is the most potent, with HIF-2? IC50 = 0.7M. K1299 treatment inhibits the growth of CRCC xenografts in mice, and decreases the levels of HIF-2? within the tumor. Additionally, plasma ferritin (which also contains a 5? IRE) serves as a pharmacodynamic (PD) biomarker for K1299. K1299 is well-tolerated in mice with no detectable signs of toxicity (including liver or kidney toxicity) after 11 days of continued dosing at 100mg/kg. We aim to show that this novel strategy for the selective depletion of HIF-2? protein will provide benefit to patients with CRCC. Our goal is to produce a novel (i.e. patentable) series of related compounds with improved potency and desirable in vivo characteristics to assess the feasibility and commercial potential of this therapeutic approach. Our first aim is to synthesize novel derivatives of our lead series for in vitro characterization through multiple rounds of iterative SAR. These will be based on our initial HTS and predicted to have improved in vivo characteristics. Compounds will be subjected to in vitro HIF-2 activity screens, as well as preliminary in vitro ADME-Tox studies. Promising compounds from this aim will be channeled to Aim 2 for in vivo characterization including additional PK/PD studies, CRCC anti-tumor studies, and further toxicity/metabolic characterization for the most promising compound. At the end of the project, we will have identified at least one novel compound with enhanced anti-tumor activity and biomarker validation, with preliminary toxicity analysis to facilitate transition to Phase II.